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Electric or AC motor and DC motor

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Topic includes 

- Electric motor
- Ac motor
- Ac motor different types
- DC motor 
- DC motor types 
- DC machine with all parts

Electric Motor


Definition: 

Electric motor is the electro-mechanical machine which converts the electrical energy into mechanical energy. In other words, the devices which produce rotational force is known as the motor. The working principle of the electric motor mainly depends on the interaction of magnetic and electric field.The electric motor is mainly classified into two types. They are the AC motor and the DC motor. The AC motor takes alternating current as an input, whereas the DC motor takes direct current.

AC Motor


The AC motor converts the alternating current into mechanical power. It is classified into three types; they are the induction motor, synchronous motor, the linear motor.

1. Induction Motor


It is also known as asynchronous
The machine which never runs at synchronous speed is called the induction or asynchronous motor. This motor uses electromagnetic induction phenomenon for transforming the electric power into mechanical power. According to the construction of rotor, there are two types of an induction motor.

Squirrel Cage Rotor 

 The motor which consists squirrel cage type rotor is known as a squirrel cage induction motor.The squirrel cage rotor decreases the humming sound and the magnetic locking of the rotor.

Phase Wound Rotor 

 This rotor is also known as the slip ring rotor, and the motor using this type of rotor is known as the phase wound rotor.
By the phases, the induction motor is classified into two types. They are the single phase induction motor and the three phase induction motor.

The difference between  squirrel cage and wound rotor  construction lies in the construction of rotor. In squirrel cage motor a series of rotor conductors are evenly spaced around the periphery of rotor of squirrel cages with their ends short circuited by conductors in the form of end rings . But in case of wound rotor machine the winding in the rotor machine the winding in the motor will be just like that of stator and the electrical connections are made between the rotor and slip rings mounted on the shaft.

Single phase induction motor 

The machine which changes1-phase AC electric power into mechanical power by using an electromagnetic induction phenomenon is known as a single phase induction motor.

The magnitude of starting torque of single phase induction motor is zero.

Single phase motors are not self starting
As it's construction is similar as 3 phase except that the stator is provided with a single phase winding . Due to this, an alternating flux acting on a stationary squirrel cage rotor cannot produce rotation.
Split phase capacitor type single phase induction motor used in ceiling fan.


Three-phase Induction Motor  

The motor which converts 3-phase AC electric power into mechanical power, such type of motor is known as a three-phase induction motor.

It is most popular type of ac motor. It is very commonly used for industrial drives since it is cheap , robust, efficient and reliable.

2. Linear Motor

The motor which produces the linear force instead of the rotational force is known as a linear motor. This motor has unrolled rotor and stator.

Such type of motor is used on sliding doors and in actuators.
It is special type of induction motor
It is in simplest form, consists of field system having a 3 phase distributed winding placed in slots .
The field system may be single or double primary system. The secondary of this type of Induction motor  is normally is conducting plate made of either copper or aluminium in which interaction currents are induced .
The ferromagnetic plate, in a single primary system is usually placed on the other side of the conducting plate to provide a path of low reluctance to the main flux.

Synchronous Motor

It is one type of  3 phase ac motor.
The machine that changes the alternating current into mechanical power at the desired frequency is known as the synchronous motor. In the synchronous motor, the speed of the motor is synchronised with the supply current frequency.

synchronous speed is measured regarding the rotation of the magnetic field, and it depends on the frequency and the poles of the motor. The synchronous motor is classified into two types they are reluctance and the hysteresis motor.


Reluctance Motor 

The motor whose starting process is similar to an induction motor and which runs like a synchronous motor is known as the reluctance motor.

Hysteresis Motor 

The hysteresis motor is the type of a synchronous motor which has the uniform air gap and does not have any DC excitation system. The torque in the motor is produced by the hysteresis and the eddy current of the motor.


DC Motor


A machine that converts the DC electrical power into mechanical power is known as DC motor. Its work depends on the basic principle that when a current carrying conductor is placed in a magnetic field, then a force exerted on it, and torque develops.
In DC motor, commutator is necessary that the current through coils of armature winding be reversed as a particular coil leaves one pole crosses the neutral line and comes under the influence of next pole which is oppositely charge.


The DC motor is classified into two types, i.e., the self-excited motor and separately excited.


1. Separately Excited Motor

The motor in which the DC winding is excited by the separate DC source is known as the separately excited dc motor. With the help of the separate source, the armature winding of the motor is energised and produce flux.

2. Self-Excited Motor

By the connection of field winding the Self-excited DC motor is further classified into three types. They are the series, shunt and compound wound DC motor.

Shunt Motor 

The motor in which field winding is placed parallel with the armature, such type of motor is known as shunt motor.

Series Motor  

In this motor the field winding is connected in series with the armature of the motor.

Compound Wound Motor 

The DC motor which has both the parallel and series connection of the field winding is known as the compound wound rotor. The compound wound motor is further categorised into short-shunt and long-shunt motor

Short Shunt Motor  

If the shunt field winding is only parallel to an armature of the motor and not the series field, then it is known as the short shunt connection of the motor.

Long Shunt Motor 

If the shunt field winding is parallel to both the armature and the series field winding then the motor is known as the long shunt motor.


DC machine

In generator the end induced in armature and is rotated with help of external means.
In motor, the DC supply is given to field and armature is rotated with the help of commutator and brushes.

Yoke

It is the outermost part of the machine. For small machines, it is made up of cast iron and for large machines, it is made up of fabricated steel. It provides mechanical protection to the inner part of machine. It also provide low reluctance part for field flux.

Pole core


It is made up of laminated silicon steel. It accommodates field winding. It provides low reluctance path for field flux.

Pole shoe

It is made up of laminated silicon steel . It is used to provide uniform flux distribution.

Field winding

It is made up of copper wire having number of turns and placed around the pole core. The DC supply is given to it to produce main field flux. 

Armature

It is the rotating part of the machine having number of slots on the outer periphery of it. And armature winding are placed in these slots .
It is made up of silicon steel to reduce losses. 

Winding


Lap winding in which number of parallel path is equal to number of poles..
It has low voltage high current

Wave winding in which number of parallel path is equal to turn.
It has high voltage low current.

Commutator

These are the copper segments mounted on the armature to which armature winding or conductor are connected. It converts alternating current into direct current or vice versa.

Brushes

It is made up of carbon or graphite. These are placed over the commutator to supply or receive current from the rotating structure .

Shaft

It is made up of mild steel. Mechanical power is given to the shaft in generator and can be taken from the shaft in motor . 

End covers

These are the side cover of machine and also called a housing over which bearing and shaft rest.



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